1. Field of the Invention
The present invention relates generally to surgical instruments and procedures, and more particularly, to a method and apparatus for tensioning grafts or ligaments.
2. Description of the Related Art
It is well known, particularly to those who have participated in athletics, that the knee is prone to injury. Most laymen, however, consider the knee a simple hinged joint where in reality the knee provides a rather complex motion which includes not only flexion and extension, but small amounts of inward and outward rotation. In flexion and extension, the mechanical movement includes a gliding and rotation in addition to the hinging motion such that one part of the articular surface of the distal femur or proximal tibia is not always applied to the same part of the corresponding articular surface. For example, under conditions of extreme knee joint flexion, the posterior parts of the articular surfaces of the tibia have been observed to contact the femur posterior around the extremities of the condyles. If the knee where a simple hinged joint, the axis around which the revolving movement of the tibia would occur would be in the back portion of the condyle. With movement of the knee joint from flexion to semi-extension, the upper surface of the tibia will seem to glide over the condyle of the femur, such that the middle-part of the articular facets are in contact, and thus, the axis of rotation has now shifted forward to near the center of the condyle. When the knee joint is fully extended, still more gliding occurs resulting in still a further forward shift of the axis of rotation. In addition, knee joint flexure is also accompanied by a certain amount of rotation about a vertical axis drawn through the head of the tibia due to the greater length of the internal condyle and the oblique outward incline of the anterior portion of the articular surface.
The motion of the knee joint is controlled in part by the anterior and posterior cruciate ligaments (the ACL and PCL, respectively). The ACL and PCL are two very strong ligaments that cross within the knee joint and act to stabilize the knee joint movement, particularly the rotation and gliding movements described above. The ACL is attached to the anterior intercondylar area of the tibia and passes upward, backward and laterally to the lateral femoral condyle where it is attached. The PCL is attached below to the posterior intercondylar area of the tibia and passes upward, forward and medially and to the medial femoral condyle where it is attached.
The above sets forth only a brief summary of the complex nature of knee joint flexure and extension. It should, however, be apparent from the foregoing discussion that the repair of the knee ligaments, and particularly the ACL and PCL, is of significant importance to the functioning of the knee. However, surgically repairing an injury to the ligaments of the knee, and particularly the ACL and PCL, requires precise positioning and tensioning of the repair ligament. One procedure for arthroscopic repair of ligaments, and particularly the anterior and posterior cruciate ligaments, is disclosed in U.S. Pat. No. Re. 34,293 which is hereby expressly incorporated herein by reference. The procedure described in this reference provides for the precise positioning of a graft or prosthetic ligament across the knee joint. Such positioning is accomplished by forming a tunnel passing through the approximate ruptured ligament tibial and femoral points of origin and attaching a graft or prosthetic ligament therein. In addition, U.S. Pat. No. 5,037,426, which is also expressly incorporated herein by reference, discloses a method and apparatus for simply and easily verifying the isometry of the graft or prosthetic ligament. This is accomplished by securing a suture within the tunnel and measuring changes in tension in the suture as the knee joint is moved through a range of motion.
While the procedures described in the aforementioned references provide for precisely locating and verifying the position of the repair ligament across the knee joint, they do not provide a method and apparatus for setting and maintaining the tension on a graft or a ligament as it is secured across the joint. In particular, the procedure described in the U.S. Pat. No. Re. 34,293 provides only for positioning and securing a repair ligament within the knee joint as described above. The procedure disclosed in United U.S. Pat. No. 5,037,426 provides for testing the isometry of the tunnel formed in the knee joint and through which a repair ligament will be secured. The references, however, do not disclose an apparatus for tensioning the actual repair ligament as it is secured within the knee joint.